1. Field of the Invention
This invention relates to valves, specifically those valves known as plug valves. Plug valves have a rotating element called the plug, in the shape of a truncated cone with a hole through it. By rotating the plug a quarter turn, the valve can be opened or closed by aligning or mis-aligning the hole through the plug with the pipeline.
2. Background Information
The purpose of the plug valve is to contain fluid within the pipeline, exercise control over the starting and stopping of the fluid in the pipeline, hold the internal pressure within the plug valve, and prevent leaks to the surrounding environment. Prior art uses heavy spring forces to hold the plug against the body of the valve to ensure that the plug valve is leak tight. Plug valves are very hard to open and close because of the large spring forces employed to overcome unbalanced internal forces within the plug valve. Because the plug is tapered, there is slightly more area on top of the channel through the plug than on the bottom of the channel. See FIG. 1. As a result, the internal pressure produces an unbalanced force caused by the pressure acting on the larger area and this unbalanced force acts toward the larger end of the plug. It tends to try to push the plug away from the body of the valve, which, if allowed to happen, would allow leaking of the valve through the seat. To overcome this force unbalance, a somewhat higher spring force is needed. Since opening torque depends on the spring force, a larger spring force results in a higher torque required to open and close the valve. This level of torque makes it difficult to open and close the valve, especially by women or disabled workers. When an actuator is used to open and close the valve, usually a large, expensive actuator is needed. Clearly, a means is needed to lower the required torque on a plug valve while maintaining the valve leak tight.
A step is fabricated on the large end of the plug. See FIG. 2. A special secondary seal is located at approximately half the radius of the large end of the plug on the step. This is called a Veri-Seal. Internal pressures act on the area of the step create a force that is nearly equal in magnitude to the unbalanced pressure force acting within the channel and acting in the opposite direction. By careful placement and sizing of a step and location of the Veri-Seal on the large end of the plug, all internal pressures are balanced. This eliminates the need to have extremely high spring forces to overcome the unbalanced internal pressures and subsequent high opening and closing torque.